Bosch 125FX LP - Manual (Page 5)

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COMBUSTION AIR REQUIREMENTS
The AquaStar water heater holds cold water in its copper
heat exchanger and brass water valve when not in use.
Because of this, any cold air that comes in through the
unit’s vent pipe is capable of freezing these components.
This Installation Manual specifies the vent length
requirements and the amount of combustion air required for
this unit. When all requirements are followed, the unit will
operate properly and safely. However, there may still be a
risk of freezing due to negative draft if all the combustion
appliances in the area are not being supplied with a sufficient
amount of make-up air. A wood stove or furnace can rob the
make-up air in the AquaStar’s vent pipe, leaving the cold
infiltrating air capable of freezing the cold water in the
AquaStar heat exchanger. To prevent this the FXHOOD
horizontal vent terminator, which is supplied separately with
the water heater, needs to be installed on the end of the
horizontal vent run (see page 7). The FXHOOD is a CSA
approved vent terminator for the Aquastar 125FX and has a
built in back draft flapper.
Observe the following instructions concerning combustion
air.
Appliances located in unconfined spaces:
a) An unconfined space is one whose volume is greater
than 50 cubic feet per 1000 Btu per hour of the combined
rating of all appliances installed in the space. That would
be 6500 cubic feet for the AquaStar 125FX alone.
b) In unconfined spaces in buildings of conventional frame,
masonry, or metal construction, infiltration is normally
adequate to provide air for combustion, ventilation, and
dilution of flue gasses.
Appliances located in confined spaces: The confined space
must be provided with two permanent openings, one
commencing within 12 inches of the top and one
commencing within 12 inches of the bottom of the enclosure.
Each opening must have a minimum free area of one square
inch per:
— 1000 Btu/hr if all air is taken from inside the building.
— 2000 Btu/hr if all air is taken from the outside by horizontal
ducts.
— 4000 Btu/hr if all air is taken from the outside by direct
openings or vertical ducts.
Or the confined space must be provided with one permanent
opening or duct that is within 12 inches of the ceiling of the
enclosure. This opening must have a minimum free area of
one square inch per:
— 3000 Btu/hr if all air is taken from the outside by a direct
opening or vertical duct.
Louvers, grills and screens have a blocking effect. If the
effective free area is not known, assume it is 20 % to 25%
of the total opening for wood louvers and 60 % to 75% for
metal louvers. Refer to the National Fuel Gas Code for
complete information. In buildings of tight construction all
air should be taken from outside.
This product is not approved for manufactured homes
(mobile home), recreational vehicles (RV) or boats.
Reference ANSI Z21.10.3.
This product is neither designed or approved for outside
installations.
CLEARANCES
The Aquastar 125FX is design certified for installation on a
combustible wall and for installation in an alcove or closet
with the minimum clearances to combustible and non -
combustible construction listed below
A. Top 12 inches (305 mm)
B. Front 4 inches (102 mm)
C. Back 0 inches*
D. Sides 4 inch (102mm)
E. Bottom 12 inches (305 mm)
* On a combustible wall surface the unit should be mounted
away from the wall to provide adequate clearance of the
vent pipe. Clearance from the vent pipe is dependent upon
the clearance rating of the venting material used. See
VENTING section.
125FX Air Vents
(5 ½ X 5 ½ in. each)
Air Vents
(10 ¾ X 10 ¾ in. each)
125FX